Bring back a deprecated AndroidHarness to make it easier to move to 3.10 #2765

In #2727 AndroidHarness was removed entirely. We should bring back AndroidHarness, based on top of the new fragment code, to allow people to migrate to 3.10 easier, and later fix up their app to not use the deprecated code path on their own time.

Risk: the new migration friendly deprecated AndroidHarness won't be exactly the same as the old code path, though the API should be, so we will need testing from users with real apps.